RFR: 8270836: Foolproof JavadocTester.checkOutput

[Pavel Rappo]

When searching output for multiple strings it is easy to misexpress your intent, which could make a failing test pass. Such cases can be caught and reported to the programmer.

For example, for this search to succeed it is sufficient for the output to consist only of the `"error: bad"` string:


checkOutput(..., "error:", "error: bad", ...)

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/4811/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4811&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270836
  Stats: 92 lines in 2 files changed: 91 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4811.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4811/head:pull/4811

PR: https://git.openjdk.java.net/jdk/pull/4811